Array Search

Array Search

Arrays have several methods for finding items.

indexOf

Finds the first position of a value, or -1:

["a", "b", "c"].indexOf("b"); // 1
["a", "b"].indexOf("z");       // -1

includes

Checks if a value exists, returning true/false:

["a", "b"].includes("a"); // true

find and findIndex

• find returns the first matching item.
• findIndex returns the index of the first matching item.

[10, 20, 30].find(n => n > 15);      // 20
[10, 20, 30].findIndex(n => n > 15); // 1

lastIndexOf

Finds the last position of a value:

[1, 2, 1].lastIndexOf(1); // 2

indexOf vs includes

• Use includes when you only need to know "does it exist?".
• Use indexOf when you need the position.

TL;DR

• indexOf finds the first position or -1.
• includes checks existence.
• find returns the item; findIndex the index.
• lastIndexOf finds the last position.